Biological electrochemical systems (BESs) have the potential for decentralized treatment in developing countries. A 46 L, two-chamber, hydraulically partitioned microbial fuel cell (MFC) was designed to replicate low-flow scenarios leaving a composting toilet. The co-evolution of electricity and methane in this MFC was evaluated by testing two distinct waste streams: synthetic feces (Case F) and municipal primary effluent (Case W). Oxidation of organic matter was 76 ± 24% during Case F and 67 ± 21% during Case W. Methanogenesis was dominant in the anode, yielding potential power of 3.3 ± 0.64 W/m3 during Case F and 0.40 ± 0.07 W/m3 during Case W. Electrical power production was marginal, Case F = 4.7 ± 0.46 and Case W = 10.6 ± 0.39 μW/m3, although potentially useful in energy-limited areas. Complimentary batch cultivations with anode inocula yielded greater methane production in the presence of graphite. 74 ± 11% more methane was produced with graphite than suspended growth enrichments and 58 ± 10% more than enrichments with non-conductive plastic beads. The co-production of methane and electricity in an MFC may have utility in decentralized treatment. Further work is needed to optimize power from both electricity and methane.